Fluid systems for wheel loaders, forklift trucks, container handling machines and other machines or equipment are equipped with a prime mover for driving a fluid pump for instance via a gearbox. A problem with such a system is that the peak pressure is limited to the maximum fluid pressure supplied by the pump.
A prime mover is often connected to the pump or motor via a gearbox or a similar transmission arrangement, in order to achieve a desired rotational speed for driving the pump. When specifying a transmission system, the systems designer may have a problem, as both the transmission and the prime mover, such as an engine or electric motor, have to be sized for peak demands from the driven implement.
If the peak torque supplied to the pump is insufficient for providing the required fluid pressure to drive the implement, the result may be that the implement may not be able to support its load. This is at best annoying for the operator but could under certain conditions create a dangerous situation. If the torque supplied by the prime mover is too high, then the torque may exceed the maximum torque allowed by the gearbox manufacturer. During peak loading this could cause the gearbox to fail. This has resulted in many machine manufacturers selecting larger gearboxes than actually needed for the drive. For the same reasons, the size of the prime mover can also be oversized in relation to the average power required.
The invention aims to overcome the above problems by providing an improved hydraulic system that will make it possible to downsize transmissions and in some cases also the prime mover, while still being able to supply the peak torque demand required by the system.